The Marfan syndrome, a prototype of heritable diseases of connective tissues, clearly involves aberrations in the extracellular matrix of the connective tissue, yet the underlying molecular defect(s) is unknown. In this grant application, we are proposing a concentrated, multidisciplinary effort to study the biochemistry of connective tissue in the Marfan syndrome. The experiments are designed to test the hypothesis that a structural or metabolic alteration in collagen and/or elastin is the underlying defect. The main emphasis of these studies will on detailed elucidation of the biochemical defect of elastin in Marfan syndrome, based on our previous demonstration of reduced concentrations of desmosines, elastin-specific cross-link amino acids, in elastin isolated from aortae. Two different approaches will be utilized: First, tissues, such as aorta and skin, will be obtained from patients with the Marfan syndrome. For comparison, tissues from patients with dissecting aneurysm but without stigmata of the Marfan syndrome, as well as from matched controls will be obtained. The studies on elastin include additional cross-link analyses and determination of chemical composition. Second, skin fibroblasts, which we have recently shown to express elastin gene in culture, will be subjected to elastin analyses by immunoblotting and ELISA assays. Third, if evidence of a structural mutation in elastin is detected, we will apply the recombinant DNA technology to characterize the mutated sequences. Finally, the biochemical findings will be correlated to the structural organization of tissues by scanning and transmission electron microscopy. We expect that using these approaches we are able to disclose specific biochemical defects in elastic fibers, and that such defects would explain the clinical manifestation, such as fragility of connective tissues in Marfan patients.